SDL: Fixed compiling SDL_platform_defines.h on macOS with older compilers (thanks @sezero!)

From 36015ad5e58c413e8a101c48ed2bdbcdd044c868 Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Mon, 27 May 2024 14:33:18 -0700
Subject: [PATCH] Fixed compiling SDL_platform_defines.h on macOS with older
 compilers (thanks @sezero!)

Fixes #9632
---
 include/SDL3/SDL_platform_defines.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/SDL3/SDL_platform_defines.h b/include/SDL3/SDL_platform_defines.h
index 72b1ef260d5b1..e7f91cf94c9c3 100644
--- a/include/SDL3/SDL_platform_defines.h
+++ b/include/SDL3/SDL_platform_defines.h
@@ -65,7 +65,13 @@
 #define SDL_PLATFORM_APPLE  1
 /* lets us know what version of macOS we're compiling on */
 #include <AvailabilityMacros.h>
+#ifndef __has_extension /* Older compilers don't support this */
+#define __has_extension(x) 0
 #include <TargetConditionals.h>
+#undef __has_extension
+#else
+#include <TargetConditionals.h>
+#endif
 
 /* Fix building with older SDKs that don't define these
    See this for more information: